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CHICAGO (AP) – Hours after the city of Chicago released audio-free dashcam video of a white officer shooting a black teen 16 times, a 35-second excerpt with sound appeared online.

Viewers could see and supposedly hear Officer Jason Van Dyke firing nine rapid shots at Laquan McDonald, pausing for nearly 10 seconds, then firing seven more as McDonald lay on the ground.

This video, which garnered nearly half a million views on social media, added further fuel to already simmering suspicions that police were covering something up, given Van Dyke was charged with first-degree murder on Nov. 24 – more than a year after the shooting.

But experts, city police and an Associated Press analysis concluded the video is bogus.

Ed Primeau, a Michigan-based audio and video forensics expert with 32 years in the field, examined it at his lab and concluded: “It s fake. Hands down.”

Here are some reasons why he and others are convinced the audio is doctored:

GUN SHOTS

The gunfire sounds seem to match up with parts of the video, including with dust or dirt puffing into the air as bullets strike McDonald or the ground. But the shots sound more like synthesized drums than the rippling crack of the 9mm gun that, according to the charges against him, Van Dyke used.

The shots also don t sound as they should if recorded by dashcam-system microphones, Primeau said, because they don t reverberate or vary in frequency as they should. It s likely, he said, that the same sound was used for all the shots in the video. “The frequency decay of the gunshot, timbre or sound of the gunshot, as well as duration of the sound are almost identical,” he said.

VOICES

The sound of officers speaking over their radios is also suspect, Primeau argued, citing sections where exactly the same words and sounds are duplicated and dubbed in. If a microphone picked up the sound of shots, he said, you d expect it to also capture the voices of officers shouting at McDonald or each other.

At places in the video, officers also appear to move their mouths but there s no corresponding sound on the suspect video, said Primeau, who also serves on the executive committee of the American Board of Recorded Evidence.

POLICE WEIGH IN

Chicago Police Department spokesman Anthony Guglielmi said its in-house experts also determined the audio is not authentic. The “garbled talking in the background apparently does not match this incident,” he said in a statement. And, he said, “this type of recording would not be possible from the in-car camera system” that Chicago police use.

To make clear that police bias didn t influence that finding, Guglielmi has said the department would send the questionable audio-video clip “to an independent third-party to validate the findings of our forensic team.”

WHO POSTED THE VIDEO?

That s not at all clear. The original source used the handle “Daily News Hub” to post it on YouTube – a handle that had posted no prior videos and that linked to a Twitter profile with only one tweet from June 2014. The owner of the accounts did not respond to requests for comment.

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